Cathode ray tube screen having contiguous,overlapping color areas

ABSTRACT

A color picture tube with a shadow mask provided therein, in which tri-color phosphor dots, constituting the screen of the tube, are arranged such that the centers of the adjoining dots are located at the apices of a regular triangle and two of them overlap each other, and a light absorbing material is coated on said overlapping area.

United States Patent 1 Oikawa [451 July 10, 1973 CATHODE RAY TUBE SCREEN HAVING CONTIGUOUS, OVERLAPPING COLOR AREAS [75] Inventor: Mitsuru Oikawa, Tokyo, Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: July 1, 1970 [21] Appl. No.: 51,438

[30] Foreign Application Priority Data July 4, 1969 Japan 44/5248! [52] US. Cl. 313/92 B, 96/36.] [51] Int. Cl. H01] 29/30, 1-101j 39/20 [58] Field of Search 313/92 B, 85 S [56] References Cited UNITED STATES PATENTS 3,569,761 3/1971 Lange 313/85 S X 2,631,253 3/1953 Law 313/92 B X 3,146,368 8/1964 Kaplan 313/92 B 3,344,301 9/1967 Kaplan 313/92 B Primary Examiner-Robert Segal Attorney-Craig, Antonelli & Hill [5 7] ABSTRACT A color picture tube with a shadow mask provided therein, in which tri-color phosphor dots, constituting the screen of the tube, are arranged such that the centers of the adjoining dots are located at the apices of a regular triangle and two of them overlap each other, and a light absorbing material is coated on said overlapping area.

5 Claims, 3 Drawing Figures PATENTED 0'975 3. 745. 398

INVENTOR MITSURU O l KAWA BY Gag, nlzmm, Stwml: mu

. ATTORNEY! CATHODE RAY TUBE SCREEN HAVING CONTIGUOUS, OYERLAPPING COLOR AREAS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a color picture tube and more particularly to such a color picture tube in which a light absorbing material is coated on each of the overlapping border portions of the tri-color phosphor dots.

2. Description of the Prior Art The fluorescent screen of a conventional color picture tube is formed by coating tri-color phosphor materials of red (R), green (G) and blue (B) in the form of dots, in such a manner that the centers of the adjoining phosphor dots are located at the apices of a regular triangle and the dots are substatnailly in contact with each other at the peripheral edges thereof. Therefore, a shadow mask having beam passage apertures perforated therein is provided in front of the fluorescent screen to ensure that electron beams modulated by R, G and B chrominance signals for the respective dots will not impinge upon the phosphor dots of other colors to emit a light or, in other words, the color purity will not be degraded. The diameter of the phosphor dots is, for example, 0.4 mm, whereas the diameter of the beam passage apertures in the shadow mask is, for example, 0.28 mm. It will, therefore, be seen that only about 49 percent of the total area of the phosphor dot (or about 70 percent of the diameter of the phosphor dot) is effectively used for the emission of light. This is for the purpose of providing an allowance for deviation of the electron beam and thereby improving the color SUMMARY OF THE INVENTION An object of the present invention is to' provide a color picture tube which is excellent inbrightness as well as in color purity.

Another object of the invention is to provided a color picture tube in which the electron beam utility is high.

In order to attain the objects as abovedescribed, one form of the color picture tube according to the invention comprises an electron gun to generate electron beams, a shadow mask and a fluorescent screen which undergoes bombardment of the electron beams through said shadow mask, said fluorescent screen comprising tri-color phosphor dotsluminous in red, green and blue colors respectively and arranged in such a manner that the centers of the adjoiningthree dots are located at the apices of a regular triangle and the adjoining two dots partially overlap each other, and a light absorbing material layer is coated at least on said overlapping area.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a color picture tube, partially shown in cross-section.

FIG. 2 is an enlarged view of a portion of a conventional fluorescent screen.

FIG. 3 is an elarged view of a portion of a fluorescent screen according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a color picture tube which generally comprises a glass bulb 1 which is sealed air-tight, an electron gun 2 for generating electron beams 3, a screen 4 comprising a tri-color coating layer, an anode electrode 5 simultaneously serving as a metal back layer, a shadow mask 6 having electron beam passage apertures perforated therein, a terminal 7 for impressing an anode voltage on the shadow mask and the anode electrode, and a deflection coil 8 for deflecting the electron beams.

In the construction described above, the screen 4 comprising a coating layer of tri-color fluorescent materials has heretofore been formed as shown in FIG. 2. Namely, the centers of the adjoining R, G and B phosphor dots are located at the apices of a regular triangle and these phosphor dots are in contact with each other at their peripheral edges. The radius of the phosphor dots is represented by r The conventional color picture tube has the disadvantages as described previously, because of such a structure.

FIG. 3 shows the structure of a screen according to the present invention, in which R (red), G (green) and B (blue) are tri-color phosphor dots of a substantially polygonal shape having inwardly concaved, sides respectively and arranged with the centers thereof located at the apices of a regular triangle, and the circumscribed circles of the respective dotshave such a radius as will enable said circumscribed circles to overlap each other, With r 'representing the radius of the circumscribed circles of the phosphor dots (usually phosphor elements) according to the invention, it is stated that: i

Namely, the tri-color phosphor dots of the present invention have such a size that the circumscribed circles of the phosphor dots R, G and B pass the center of gravity c of a regular triangle, each side of which is 2r in length and on the apices of which the centers of said phosphor dots are located respectively. The area defined by the circumscribed circle, which is generally larger than the phosphor element, will hereinafter be referred to briefly as an area in which the phosphor element is positioned. The portion of each phosphor dot of the invention which emits a light, is not circular in shape, and the overlapping portion of the circumscribed circles of the adjacent phosphor dots (the hatched portion in FIG. 3) is coated with a non luminous substance (e.g. powdered carbon or manganese dioxide). Therefore, the above-described portion of the phosphor dot has a unique polygonal shape (a hexagonal shape in the illustration) which is inscribed within a circle having a radius of r (1.16 r,,) and the sides of which are concaved inwardly.

By forming the fluorescent screen in the manner described above, it is possible to increase the brightness of a picture image and to improve the color purity of the same. This will be explained hereunder:

In the conventional color picture tube, the diameter of the beam spots are selected to be about percent of the diameter of the tri-color phosphor dots, so as to provide an allowance for deviation of the electron beams. When the diameter of the beam spots is similarly selected to be about 70 percent of the diameter of the circumscribed circles (the radius is r,) of the phosphor dots in the present invention, the size S, of the beam spot is represented by the following formula:

On the other hand, the size S of the beam spot (which is 49 percent of the area of the phosphor dot) in the conventional color picture tube is represented by the following formula:

S 'zrf X 0.49 0.49 7m,

Thus, from formulas (2) and (3) above, the light emitting area ratio L, between the present invention and the prior art is:

L r /0.49 r 1.3

This means that, by the use of the screen according to the invention, the area of each of the beam passage apertures in the shadow mask can be increased to about 1.3 times that of the beam passage aperture in the prior art shadow mask and the present transmission of the beam can be increased accordingly, i.e. the brightness of the picture image can be increased.

The radius r and the area S; of the inscribed circle of the phosphor dot (unique hexagonal shape) according to the invention are respectively represented by the following formulas:

r 2r r 2r 1.16r 0.84r

Thus, from formulas 2) and (6), the ratio L of the effective light emitting area of the total area of the phosphor dot is:

L, s,/s, x 100 93 percent This is a remarkable improvement over the value of 49 percent which is the effective light emitting area ratio of the conventional phosphor dot.

It is also to be noted that according to the present invention, since the diameter of the beam spot is set at about 70 percent of the diameter of the circumscribed circle of the phosphor dot, similar to the prior art screen, the color purity is not degraded, even through the area of the beam spot is increased to 1.3 times that of the beam spot on the prior art screen, but is rather improved because the area overlapping the area in which the adjacent phosphor dot is positioned, is coated with a non-luminous substance.

It is also to be noted that when a black color substance, e.g. carbon, is used for the non-luminous substance to be coated on the overlapping portion of the circumscribed circles of the adjacent phosphor dots, an

external light is absorbed to some extent by said substance, so that the light reflecting on the face panel can be decreased. Therefore, according to the present in vention there is the advantage that the transparency of the hitherto used face glass can be improved and hence the brightness of picture image can be increased.

Now, a method of producing the flurescent screen of the invention as described above will be briefly explained hereunder by way of example:

In the production of the fluorescent screen, the ultraviolet ray exposure method can be used which has been used heretofore for the production of color cathoderay tubes. Namely, a powder of a non-luminous substance (e.g. powdered carbon) is coated on the inside surface of the face panel of a cathode-ray tube, by dispersing it in a polyvinyl alcohol solution with ammonium dichromate (photosensitive material) added thereto. The coating layer of the non-luminous substance thus formed is exposed to ultraviolet rays through a shadow mask, as has been practiced heretofore. In this case, the shadow mask used has apertures which are larger than those in a shadow mask previously used (e.g. apertures of a diameter about 1.6 times that of the latter) and further a condensing lens is used which makes it possible to produce a circular spot exposed to ultraviolet rays through the shadow mask which has a radius of 2r,,/ {3 wherein r represents the radius of the prior art dot. The exposure is effected by irradiating concurrently the entire area of the coating layer from three light sources which are set in the position of the electron gun within the cathode-ray tube and arranged at the apices of a regular triangle respectively, and which, as a whole, approximate a point source of light. By so doing, the hatched portions in FIG. 3 are exposed dually. In this case, the intensity of light from the three light sources and the time of exposure are so suitably adjusted that the portions only of the coating layer which have been dually exposed may be sensitized and become soluble in water, with the other portions remaining unsensitized, or, for example, the overlapping portions may be exposed to an exposure of 6 KLM (wherein KL is an abbreviation of kilolux and M stands for minute) and the other portions may be exposed to a half of said exposure. After exposing the coating layer in the manner described, the coating layer is washed with water, whereby the dually exposed portions (the hatched portions in FIG. 2) only remain, with the other portions being washed away.

By the process described above, a screen can be formed in which the overlapping portion of two of the circumscribed circles of the three adjacent R (red), G

are formed on the screen by a method which is exactly the same as the ultraviolet ray exposure method commonly used in the art and, therefore, will not be described herein. In the step of forming the tri-color phosphor dots, a shadow mask is used for exposure which, similar to that mentioned above, has apertures of a diameter about 1.6 times that of the apertures in the conventionally used shadow mask. Therefore, it will be understood that two types of fluorescent materials will be coated on each of the non-luminous coating layer one on top of another and hence said coating layer will emit a light under bombardment of the electron beams. However, the light emitted by the fluorescent material on top of the non-luminous coating layer projects toward the electron gun and does not project toward a viewer by reason of being intecepted by the nonluminous coating layer. Therefore, the color purity will not be degraded. With r representing the radius of the phosphor dot to be coated, said radius may be selected within the range of r 5 R r Where the radius of the desired phosphor dots (usually the phosphor element) is smaller than the radius of the above-mentioned circumscribed circles of phosphor dots, the diameter of the apertures in the shadow mask, which was used for exposure in the formation of the non-luminous coating layers, is reduced, for example, to about 1.3 times that of the apertures in the conventionally used shadow mask, by forming on the peripheral surface of each aperture a layer of plating of such material as aluminum or nickel with which a plating can easily be obtained. If the shadow mask (having apertures of a size about 1.6 times that of the apertures in the conventionally used shadow mask) which was used in the formation of the non-luminous coating layers, is used as his, as a shadow mask to be incorporated in the cathode-ray tube, the diameter of the beam spots will become undesirably large, degrading the colorimetric purity. Therefore, a shadow mask is used whose aperture size has been reduced (to about 1.3 times that of the conventionally used one) as by plating, or a postfocusing method, well known in the art, is employed.

Although in the embodiment described above the exposure is effected by the use of a shadow mask having circular apertures therein, it is to be understood that the exposure may similarly be effected by the use of a shadow mask having hexagonal apertures. In this case, the non-luminous coating layer is formed in the shape of a hexagonal ring and the phosphor element is also of a hexagonal shape.

As has been described in detail herein, it is possible according to the present invention to enhance the utility of electron beams, to increase the brightness of a viewing panel and to obtain an image excellent in color purity, and hence the invention is of great advantage.

1. In a three-gun type color picture tube having a triad-type fluorescent screen, said screen being subdivided into a plurality of contiguous generally hexagonal areas each assigned to one of the three different primary colors, the respective generally hexagonal areas being arranged in zones of three areas each assigned to a different primary color and each of the generally hexagonal areas being located within a circle circumscribed thereabout, which circles are positioned at the apices of a regular triangle and have respectively a radius of r, that is defined by r r 5 1.16m, where r is one half of a side of said regular triangle, whereby the respective adjacent circles circumscribed about said generally hexagonal areas partially overlap each other to from therebetween an overlapped region, respectively;

said screen comprising:

i. a coating layer of a non-luminous substance covering said overlapped regions; and

ii. three different color phosphor elements each luminous in one of three different primary colors covering the generally hexagonal areas of each triangle as assigned, respectively.

2. A color picture tube according to claim 1, wherein said three different color phosphor elements are formed within the respective circumscribed circles in the assigned generally hexagonal areas, respectively.

3. A color picture tube according to claim 1, wherein each of said generally hexagonal areas has an inscribed circle therein whose radius is not less than 0.84r

4. A color picture tube according to claim 2, wherein each of the phosphor elements is formed within a circumscribed circle and has a circular shape whose radius r; is limited within the range of 0.84r o 5 r 5 l 1 67'0- 5. In a three-gun type color picture tube having a triad-type fluorescent screen subdivided into a plurality of contiguous circular areas of equal size entirely covering said screen, the centers of said circular areas being spaced by a distance less than the diameter of the circular areas so as to provide linked overlapped zones surrounding non-overlapped generally hexagonal zones, said screen comprising a non-luminous substance entirely covering said overlapped zones, and

three different color phosphor elements each luminous in one of three different primary colors and each entirely covering one of the non-overlapped generally hexagonal zones, said phosphor elements being arranged with their centers at the apices of regular triangles with the elements of each triangle being luminous in the three primary colors,

wherein said circular areas each have a radius r and the distance between the centers of said circular areas is r.,, wherein r r 5 l.l6r 

2. A color picture tube according to claim 1, wherein said three different color phosphor elements are formed within the respective circumscribed circles in the assigned generally hexagonal areas, respectively.
 3. A color picture tube according to claim 1, wherein each of said generally hexagonal areas has an inscribed circle therein whose radius is not less than 0.84r0.
 4. A color picture tube according to claim 2, wherein each of the phosphor elements is formed within a circumscribed circle and has a circular shape whose radius r3 is limited within the range of 0.84r0 < or = r3 < or = 1.16r0.
 5. In a three-gun type color picture tube having a triad-type fluorescent screen subdivided into a plurality of contiguous circular areas of equal size entirely covering said screen, the centers of said circular areas being spaced by a distance less than the diameter of the circular areas so as to provide linked overlapped zones surrounding non-overlapped generally hexagonal zones, said screen comprising a non-luminous substance entirely covering said overlapped zones, and three different color phosphor elements each luminous in one of three different primary colors and each entirely covering one of the non-overlapped generally hexagonal zones, said phosphor elements being arranged with their centers at the apices of regular triangles with the elements of each triangle being luminous in the three primary colors, wherein said circular areas each have a radius r1 and the distance between the centers of said circular areas is r0, wherein r0 < r1 < or = 1.16r0. 